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Old 06-19-2021, 02:39 AM   #1
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Light Switch Turns on Furnace Fan

I heard a fan noise in our RV just now - so I went in search of the source.
It appears to be coming from the furnace - however, the furnace is turned off.
The only thing I could detect that was turned on was the light switch that controls the ceiling lights down the centre of the RV.
Has anyone had this experience? Before I try to figure out what is going on.
I have not noticed this previously (we have owned the RV for 3 years) - so not sure if I just missed it or something has happened with the wiring.

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Old 06-19-2021, 03:59 AM   #2
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An additional light load can cause the converter fan to come on, or maybe a PO wired a vent fan into the light circuit? The furnace fan is VERY NOTICEABLE when it runs.
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Old 06-19-2021, 04:03 AM   #3
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The obvious question... can you feel air blowing from the furnace duct?
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Old 06-19-2021, 04:23 AM   #4
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Originally Posted by Chateau_Nomad View Post
The obvious question... can you feel air blowing from the furnace duct?
Well that is the odd thing - or one of them.
The furnace is actually turned off - or the switch to it is.
So it is not blowing air - just making a noise like something is running.
Maybe it's not the fan at all.
As soon as I turn the light switch off, the noise is gone.
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Old 06-19-2021, 04:25 AM   #5
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Originally Posted by 16ACE27 View Post
An additional light load can cause the converter fan to come on, or maybe a PO wired a vent fan into the light circuit? The furnace fan is VERY NOTICEABLE when it runs.
Yes, it is very loud when the furnace is turned on and it cuts in.
This is definitely not that sound.
It is very low in volume - and seems to be coming from the area/location of the furnace.
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Old 06-19-2021, 04:29 AM   #6
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Originally Posted by 16ACE27 View Post
An additional light load can cause the converter fan to come on, or maybe a PO wired a vent fan into the light circuit? The furnace fan is VERY NOTICEABLE when it runs.
I am thinking along the lines you suggested - a fan might be wired into the light circuit.
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Old 06-19-2021, 06:08 PM   #7
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Light Switch Turns on Fan - maybe not Furnace Related at all

I checked this morning, turned on that same light switch, and no fan noise.
Something else must have been going on, to trigger that fan - if that is what it was.
Thanks, all, for your replies - I will see if this reoccurs.
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Old 06-19-2021, 06:20 PM   #8
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Old 06-19-2021, 06:58 PM   #9
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sounds like your CONVERTER making noise...
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Old 06-19-2021, 07:11 PM   #10
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Some coaches have fans in the refrigerator circuit that are in the outside refridge compartments. They are normally thermostat controlled and come on when the sun is beating down on the refridge side of the MH. Some have also been added by dealers and may have been wired in for manual control. Our present coach is the first that we have owned with this fan so I was quite surprised when I heard it and had to investigate what it was and why it was there.
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Old 06-19-2021, 07:18 PM   #11
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I concur with 16ACE27 inverter theory.
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Old 06-19-2021, 07:48 PM   #12
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Looking at your coach's layout with the power center and CONVERTER located in the same vicinity as the furnace I really think it was the CONVERTER fan you heard. Although you may not be able to reproduce it with just turning on the cabin lights (depends on the state of battery charging occurring) if you turn on all the lights in the coach it should trigger the fan to come on.
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Old 06-19-2021, 08:18 PM   #13
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Light Switch Triggers Fan

Thank you!!
Of course we went out and turned on all of the lights - and the fan noise started.
You called it!
I am sure it is indeed the Converter Fan - appreciate that resolution - now we don't need to figure out if there is a wiring issue.
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Old 06-19-2021, 09:16 PM   #14
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Quote:
Originally Posted by laurine View Post
Thank you!!
Of course we went out and turned on all of the lights - and the fan noise started.
You called it!
I am sure it is indeed the Converter Fan - appreciate that resolution - now we don't need to figure out if there is a wiring issue.
Before worrying about wiring remove the battery/batteries & take them to your local auto parts store & have them load tested. I'm guessing they are the culprit that when you turn on the lights, especially if equipped with halogen bulbs, there's an immediate battery discharge resulting in the converter kicking on.
If they need replaced be sure, for the house batteries, they are deep cycle rv batteries. If there's CCA, CA or MCA listed on the top they aren't deep cycle but rather cranking batteries for starting vehicles suitable for the chassis battery.
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Old 06-20-2021, 04:04 AM   #15
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Originally Posted by Travelin' Texans View Post
Before worrying about wiring remove the battery/batteries & take them to your local auto parts store & have them load tested. I'm guessing they are the culprit that when you turn on the lights, especially if equipped with halogen bulbs, there's an immediate battery discharge resulting in the converter kicking on.
If they need replaced be sure, for the house batteries, they are deep cycle rv batteries. If there's CCA, CA or MCA listed on the top they aren't deep cycle but rather cranking batteries for starting vehicles suitable for the chassis battery.
Apparently we do have halogen bulbs so good to know! Our house batteries failed within a year of purchasing the RV, so we replaced them with deep cycle. Regardless, this is good information!
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Old 06-23-2021, 07:36 PM   #16
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Moisture gets on the control board from a leak around the outside access panel. The water shorts out something on the board and can cause your problem. If this is the case, open the outside panel and locate the board to remove it and dry off.
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Old 06-23-2021, 07:40 PM   #17
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Originally Posted by laurine View Post
Yes, it is very loud when the furnace is turned on and it cuts in.
This is definitely not that sound.
It is very low in volume - and seems to be coming from the area/location of the furnace.
My money is on the converter. Which probably very close to the furnace. The converter comes on every time you turn on a light switch. Is your fuse/breaker box close to the furnace???

Now that I have read thru the whole thread i see 16ACE bet me to it.
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